The present invention relates to modulation of the central nervous system by introducing a stimulus or stimuli to one or more sensory pathways and, more particularly, to modulation of neural oscillatory patterns associated with a neurological condition.
The brain is estimated to contain over 100 billion neurons and almost 1 trillion connecting synapses. To harness the amazing processing capabilities that this population gives rise to, the brain relies on communication both within and between a large and diverse group of specialized structures. These cortio-cortical regions are connected through the mechanism of synchronized neural oscillation—the rhythmic and/or repetitive electrical activity generated spontaneously and in response to stimuli by neural tissue. Functionally, neural oscillations are a prominent feature of brain activity. And, the synchronization of these oscillations, which reflects the temporally precise interaction of neural assemblies, is the putative mechanism whereby brain regions sub-serving specific functions communicate with each other in order to accomplish perception, cognition, and action.
By convention, neural oscillations, more commonly known as brainwaves, are divided into five frequency bands, each of which is believed to play a variety of distinct roles in normal brain function and, of importance to the present invention, can also be the underlying cause of neurological dysfunction.
Table of Brainwave FrequenciesFrequency RangeSymbol and Namef < 4 Hzδ (delta frequency band)4 Hz-8 Hz Φ (theta frequency band8 Hz-13 Hzα (alpha frequency band)13 Hz-35 Hz 13 (beta frequency band)35 Hz-200 Hzγ (gamma frequency band)
The role of brainwaves as the essential building blocks in sensory-cognitive processes has become a central tenet of modern neuroscience. Even simple sensory, motor and cognitive tasks depend on the precise coordination of many brain areas. And, as no behaviorally relevant task is performed independently by a single neuron, communication is of the utmost importance. Thus, ultimately, optimal brain performance relies on optimal communication.
The brain's dependency on neural oscillation and synchrony has led to the belief that the vast majority of neurological conditions are caused by defects in the brain's ability to communicate internally. Numerous clinical studies have shown that event-related oscillations in the alpha, beta, gamma, delta, and theta frequency windows are highly modified throughout the cortex in pathologic brains, particularly so in patients with cognitive impairments such as schizophrenia, autism, epilepsy and attention deficit disorder. Moreover, evidence is emerging that patterns of synchronization and de-synchronization are fundamental to the proper functioning of neural assemblies. For example, an abnormal pattern of synchronization/de-synchronization in parts of the motor system is believed to be a key pathophysiological mechanism underlying the motor symptoms, such as tremor and poverty of movement, in Parkinson's disease.
Commonly, patients with these and similar conditions are initially treated with drugs. While a large proportion of these patients may be aided by pharmaceutical interventions, many are not helped by medication, or are not helped sufficiently to provide the desired levels of relief. In these cases, more aggressive interventions, such as Deep Brain Stimulation (DBS) are often recommended.
Deep brain stimulation suffers from many disadvantages, the most obvious being the significant risks associated with open cranial surgery and the risk of damage to areas of the brain adjacent to the insertion route of the stimulation electrodes. Further, it has been shown that the electrical stimulus employed by DBS devices can damage surrounding tissue and even distal areas of the brain connected to the site of stimulation.
More recently, a number of less invasive neurostimulation technologies have become available. These technologies, most notably transcranial magnetic stimulation and transcranial electric stimulation have shown some efficacy in treating tinnitus, migraines, depression and epilepsy. However, the observed therapeutic effects of these treatments have generally not persisted for significant periods of time beyond the treatment window. And, because of safety concerns and other reasons these modalities cannot be administered outside a clinical setting, the long-term benefit of these technologies remains in question.
Therefore, there is a need to treat the foregoing example medical conditions and other neurological disorders resulting from defective neural synchrony without the use of pharmaceuticals, implanted neurostimulation devices or transcranial neuromodulation technologies.